The present invention relates to a vertical contour correcting device for a video signal utilized in a television receiver etc.
Referring to FIGS. 19, 20, 21, 22 and 23, an example of a conventional vertical contour correcting circuit will now be described. As shown in FIG. 19, the conventional vertical contour correcting device VCC has an input port 1, a vertical contour component extracting device 3, an adder 7, a non-linear processor 18, and an output port 2. The input port 1 receives input of a digital video signal S1 from an external video signal source (not shown). The vertical contour component extracting device 3 is connected to the input port 1 and extracts vertical contour components of the input digital video signal S1 to generate a vertical contour component signal S1v, and it also delays the present video signal S1 to be corrected for one line to generate a primary delayed digital video signal S1xe2x80x2.
FIG. 20 shows the structure of the vertical contour component extracting device 3 in detail. The vertical contour component extracting portion 3 includes a first one-line delay unit 19, a second one-line delay unit 20, a first coefficient unit 21, a second coefficient unit 22, a third coefficient unit 23, and an adder 24. The first one-line delay unit 19 and the first coefficient unit 21 are connected to the input port 1 to receive the input of the digital video signal S1 together. The first one-line delay unit 19 delays the digital video signal S1 by one line to generate the primary delayed digital video signal S1xe2x80x2. The first coefficient unit 21 multiplies the digital video signal S1 by a first coefficient K1 to attenuate the present digital video signal S1 and generates a first digital video sub-signal S1S. While the first coefficient K1 can take an arbitrary value, K1=xe2x88x92xc2xc in this example.
The second one-line delay unit 20 and the second coefficient unit 22 are connected to the first one-line delay unit 19 to receive input of the primary delayed digital video signal S1xe2x80x2. The one-line delay unit 20 further delays the input primary delayed digital video signal S1xe2x80x2 by one line to generate a secondary delayed digital video signal S1xe2x80x3. The second coefficient unit 22 multiplies the input primary delayed digital video signal S1xe2x80x2 by a second coefficient K2 to attenuate the primary delayed digital video signal S1xe2x80x2 and generates a second digital video sub-signal S1xe2x80x2S. As stated above, the adder 7 (FIG. 19) is connected to the first one-line delay unit 19 to obtain the input of the primary delayed digital video signal S1xe2x80x2.
The third coefficient unit 23 is connected to the one-line delay unit 20 to receive input of the digital video signal S1xe2x80x3. The coefficient unit 23 multiplies the digital video signal S1xe2x80x3by a third coefficient K3 to attenuate the digital video signal S1xe2x80x3 and generates a third digital video sub-signal S1xe2x80x3S. The above-mentioned three coefficients K1, K2 and K3 can take such arbitrary values smaller than one, such that the sum of the three coefficients is equal to zero. In this example, the values are set as K1=xe2x88x92{fraction (1/4,)} K2={fraction (1/2,)} and K3=xe2x88x92{fraction (1/4.)} The vertical contour component extracting device 3 can be a vertical filter structure providing a desired frequency characteristic.
The adder 24 is connected to the first coefficient unit 21, second coefficient unit 22, and coefficient unit 23 to receive input of the first digital video sub-signal S1S, second digital video sub-signal S1xe2x80x2S, and third digital video sub-signal S1xe2x80x3S. The adder 24 adds the three input digital video sub-signals S1S, S1xe2x80x2S, and S1xe2x80x3S which are respectively delayed for one line to generate and output the vertical contour component signal S1v to the non-linear processor 18 (FIG. 19).
FIG. 21 shows the structure of the non-linear processor 18. The non-linear processor 18 includes a coring circuit 25, a horizontal low-pass filter 26, a sequential coefficient unit 27, and a limiter 28. The coring circuit 25 is connected to the adder 24 in the vertical contour component extracting device 3 to receive input of the vertical contour component signal S1v. The coring circuit 25 then applies noise-removal to the vertical contour component of the input vertical contour component signal S1v to generate a first vertical contour component signal.
The horizontal low-pass filter 26 is connected to the coring circuit 25 to receive input of the first vertical contour component signal. The horizontal low-pass filter 26 then removes high-frequency component of the input vertical contour component signal to generate a second vertical contour component signal.
The sequential coefficient unit 27 is connected to the horizontal low-pass filter 26 to receive input of the second vertical contour component signal. The sequential coefficient unit 27 multiplies the input second vertical contour signal by a given coefficient to generate a first vertical contour correction signal.
The limiter 28 is connected to the sequential coefficient unit 27 to receive input of the first vertical contour correction signal. The limiter 28 then applies given band limitation to the first vertical contour correction signal to generate a second vertical contour correction signal S1vc.
Referring back to FIG. 19 again, as stated above, the non-linear processor 18 applies non-linear processing to the vertical contour component signal S1v outputted from the vertical contour component extracting device 3 to generate the vertical contour correction signal S1vc.
The adder 7 is connected to the first one-line delay unit 19 in the vertical contour component extracting device 3 and the non-linear processor 18 to receive input of the primary delayed digital video signal S1xe2x80x2 to be corrected and the second vertical contour correction signal S1vc. The adder 7 then adds the input vertical contour correction signal S1vc and primary delayed digital video signal S1xe2x80x2 to reproduce a vertical contour corrected video signal S1C with corrected vertical contour. The vertical contour corrected video signal S1C is externally outputted through the output port 2.
FIG. 2 shows an image represented by the digital video signal S1. In FIG. 2, the ordinate shows the vertical scanning direction Dv of the image, and the abscissa shows the horizontal scanning line direction Dh. In this image, ∘ indicates a pixel representing the image. FIG. 2 shows an example in which the digital video signal S1 is represented by pixels PA, PB and PC at three different levels.
That is to say, they are first-level pixels PA indicated by ∘ containing A, second-level pixels PB indicated by ∘ containing B, and third-level pixels PC indicated by ∘ containing C.
All pixels on the horizontal line L0 and line L1 and the pixels on the horizontal line L2 except the pixel on the vertical line xcex1 are the first-level pixels PA. The pixel on the vertical line xcex1 on the horizontal line L2 is the second-level pixel PB. All pixels on the horizontal lines L3 and L4 are the third-level pixels PC. When the levels of the pixels PA, PB, and PC are represented as Lpa, Lpb, and Lpc, they are in the relation Lpa greater than Lpc greater than Lpb. That is to say, in this case, the pixel PB on the vertical line xcex1 and the horizontal line L2 is an impulse noise. The presence of such impulse noise is likely to cause the viewers to feel as if the S/N ratio of the image is deteriorated.
FIG. 22 shows signal levels of the digital video signal S1 and the vertical contour corrected video signal S1C in the horizontal positions xcex1xe2x88x921 and xcex1+1. For the vertical contour corrected video signal S1C, ∘ with P and ∘ with N respectively indicate contour pixels PP and PN. The contour pixel PA corresponds to the contour pixel PA on the L1 line in the digital video signal S1, and the contour pixel PN corresponds to the contour pixel PC on the L3 line in the digital video signal S1. In this example, the pixel PB as an impulse noise source in the digital video signal S1 is not present in the horizontal positions xcex1xe2x88x921 and xcex1+1 as shown in FIG. 2.
Accordingly correction by the non-linear processor 18 corrects the signal level of the contour pixels without any problem. That is to say, as a result of the correction by the vertical contour correcting device VCC, the line connecting the contour pixels PP and PN after correction becomes steeper than the line connecting the pixel PA and the pixel C on the L3 line as the contour pixels of the digital video signal S1. The vertical contour of the digital video signal S1 is thus corrected and enhanced by the vertical contour correcting device VCC.
FIG. 23 shows signal levels of the digital video signal S1 and the vertical contour corrected video signal S1C in the horizontal position xcex1. For the vertical contour corrected video signal S1C, ∘ with I indicates the impulse noise source pixel PI. As shown in this diagram, the digital video signal S1 contains the impulse pixel PB at which the signal level partially projects between the vertical contour pixels PA and PC. When this digital video signal S1 is corrected in vertical contour by the vertical contour correcting device VCC, the correction by the non-linear processor 18 is uniformly applied to all pixels in the digital video signal S1.
As a result, while the signal levels of the vertical contour pixels PA (the L2 line) and PN are both raised, the signal level of the impulse noise is lowered. As a result, the slope of the line of the pixels PP-PI and that of the line of the pixels PI-PN in the vertical contour corrected video signal S1C, respectively corresponding to the line PA-PB connecting the contour pixel PA and the impulse pixel PB and the line PB-PC connecting the impulse pixel PB and the other contour pixel PC in the digital video signal S1, both become steeper than those in the digital video signal S1.
That is to say, it is seen that the impulse noise contained in the digital video signal S1 is enhanced by the vertical contour correction by the vertical contour correcting device VCC and the effect of correcting the vertical contour is deteriorated.
In this way, the conventional contour correcting device has the problems that the noise removal achieved by using the coring circuit reduces the effect of the entire contour correction, that presence of noise causes the vertical contour correction to work in opposite direction, and that the horizontal low-pass filter to the vertical contour components extends the correction in the horizontal direction.
The present invention has been made to solve the above-mentioned problems, and its object is to provide a vertical contour correcting device which reduces noise in accordance with correlation between video signals adjacent in the horizontal direction without deteriorating the effect of the entire contour correction in a vertical contour correcting device for enhancing vertical contour components of the video signal. That is to say, it corrects vertical contour enhancement by reducing the inclination of the pixels PI-PN in FIG. 23 so that the impulse noise pixel PI after the vertical contour enhancement becomes closer to the impulse noise pixel PB existing before the vertical contour enhancement. Furthermore, preferably, it adjusts the vertical contour correction to further reduce the effect of noise component by inverting the levels of the impulse noise pixel PI and the contour pixel PN after the vertical contour enhancement. In this way, its object is to provide a vertical contour correcting device which applies contour correction to an image while effectively preventing impulse noise component from being enhanced during the vertical contour correction.
The present invention is directed to a vertical contour correcting device which corrects vertical contour components of a video signal to enhance vertical contour of the video signal, which comprises:
a correlation detector for detecting correlation between a noise component contained in the video signal and the vertical contour components; and
a quantity of correction varying unit for varying the quantity of correction of the vertical contour components on the basis of the correlation;
thereby enhancing the vertical contour without enhancing the noise.
As stated above, according to the first aspect, the quantity of correction is varied in accordance with correlation between noise component contained in an input video signal and vertical contour components to correct vertical contour in accordance with the magnitude of the noise component, thus reducing enhancement of the noise by the vertical contour correction without considerably deteriorating the effect of the entire contour correction.
According to a second aspect of the invention, in the first aspect, the correlation detector comprises,
a vertical contour component extracting unit for extracting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detector for detecting correlation between the detected vertical contour components adjacent in the horizontal direction.
As stated above, according to the second aspect of the invention, the quantity of correction is varied in accordance with correlation between horizontally adjacent vertical contour components extracted from an input video signal to correct the vertical contour components by detecting presence/absence of a noise component among or in the vicinity of the contour components, thus reducing enhancement of the noise caused by the vertical contour enhancement without considerably deteriorating the effect of the entire contour correction.
According to a third aspect of the invention, in the first aspect, the vertical contour correcting device further comprises a vertical contour correcting unit for adding the corrected vertical contour components to the video signal to generate a second video signal with enhanced vertical contour.
According to a fourth aspect of the invention, in the second aspect, the horizontal correlation detector comprises,
a sign extracting unit for extracting signs of the vertical contour components adjacent in the horizontal direction, and
a sign comparator for comparing the extracted signs,
wherein the quantity of correction varying unit varies the quantity of correction when the signs of the vertical contour components adjacent in the horizontal direction are inverted.
As stated above, according to the fourth aspect of the invention, when a vertical contour component corrected in the opposite direction, due to noise, to the present video signal adjacent in the horizontal direction is extracted, the quantity of correction can be varied so as to reduce enhancement of the noise.
According to a fifth aspect of the invention, in the first aspect, the vertical contour component extracting unit further comprises a delayed video signal extracting unit for extracting a delayed video signal from the video signal by delay-adjusting the video signal,
and wherein the vertical contour correcting device further comprises a vertical contour correcting unit for varying the video signal with the varied quantity of correction to generate a second video signal with enhanced vertical contour.
According to a sixth aspect of the invention, in the first aspect, the vertical contour correcting device further comprises a vertical contour component quantity checking unit for comparing the vertical contour component with a given threshold,
wherein the vertical contour component quantity checking unit does not allow the quantity of correction varying unit to operate when the vertical contour component is smaller than the threshold.
As stated above, according to the sixth aspect of the invention, the quantity of correction varying unit is not operated when a vertical contour component inputted to the vertical contour component correlation detector is smaller than a given threshold, and therefore even if a vertical contour component corrected in the opposite direction, due to noise, to horizontally adjacent video signal is extracted, it is possible to know whether it is caused by noise or is a vertical contour component of the original video signal to set the most proper quantity of correction for the vertical contour.
According to a seventh aspect of the invention, in the fourth aspect, when the vertical contour component is smaller than the threshold, the vertical contour component quantity checking unit generates a control signal to stop operation of the quantity of correction varying unit.
An eighth aspect of the invention is directed to a vertical contour correcting device which corrects vertical contour components of a first video signal to generate a second video signal in which vertical contour of the video signal is enhanced, which comprises:
a correlation detector for detecting correlation between components adjacent in horizontal direction in the first video signal and the video signals with corrected vertical contour components; and
a quantity of correction varying unit for varying the quantity of correction of the vertical contour components on the basis of the detected correlation.
As stated above, according to the eighth aspect of the invention, a vertical contour correcting device which enhances vertical contour components of a video signal is characterized by varying the quantity of correction in accordance with correlation between horizontally adjacent present video signals and video signals with corrected vertical contour components, wherein when the vertical contour correction causes the magnitude relation between video signals adjacent in the horizontal direction to differ from that before correction, the quantity of correction can be varied to keep the linearity of the video in the horizontal direction.
According to a ninth aspect of the present invention, a vertical contour correcting device which corrects vertical contour components of a video signal with a given quantity of correction to enhance vertical contour of the video signal comprises:
a vertical contour component extracting unit for extracting a delayed video signal by delay-adjusting the vertical contour components from the video signal and the video signal;
a correcting unit for varying the vertical contour components to generate a correction signal;
an adder for adding the correction signal and the delayed video signal to generate a vertical contour corrected video signal;
a comparator for comparing magnitude relation between delayed video signal components and magnitude relation in the vertical contour corrected video signals, the video signal components adjacent in horizontal direction extracted from the detected delayed video signal and the vertical contour corrected video signal being inputted thereto; and
a controller for varying the quantity of correction of the correcting unit when the magnitude relation between the horizontally adjacent video signal components is inverse to the magnitude relation in the vertical contour corrected video signal, based on an output from the comparator.
As stated above, according to the ninth aspect of the invention, it comprises a controller for varying the quantity (K) of correction for the correcting unit when the magnitude relation between horizontally adjacent present video signals before correction is inverse to the magnitude relation between video signals after correction, and then the quantity of correction can be varied when the vertical contour correction causes the magnitude relation between horizontally adjacent video signals to differ from that before correction, thus keeping the linearity in the horizontal direction of the video.
According to a tenth aspect of the invention, a vertical contour correcting device which corrects vertical contour components of a video signal with a given quantity of correction to enhance vertical contour of the video signal comprises:
a vertical contour component extracting unit for generating a delayed video signal by delaying the vertical contour components from the video signal and the video signal;
a plurality of first delay units for sequentially delaying the vertical contour components to generate a plurality of delayed vertical contour component signals;
a minimum value detector connected to the plurality of first delay units for detecting a minimum value among the plurality of delayed vertical contour component signals; and
a correcting unit which uses the minimum value among the delayed vertical contour component signals as the quantity of correction.
As stated above, according to the tenth aspect of the invention, the minimum value is detected from among vertical contour components extracted from an input video signal by using a plurality of delay units and a minimum value detector and the detected minimum value is used as a correction signal, which reduces enhancement of noise when a vertical contour component of the video signal is much larger than horizontally adjacent pixels due to an impulse type noise which is difficult to reduce with a horizontal low-pass filter.
According to an eleventh aspect of the invention, in the tenth aspect, the correcting unit comprises,
a coring circuit for coring the minimum value of the delayed vertical contour component signals,
a horizontal low-pass filter unit for applying horizontal low-pass filter to the cored minimum value of the delayed vertical contour component signals,
a coefficient unit for multiplying the minimum value subjected to the horizontal low-pass filter by a given coefficient, and
a limiter unit for limiting band of the minimum value multiplied by the coefficient,
and wherein the vertical contour correcting device further comprises,
a plurality of second delay units for sequentially delaying the delayed video signal to generate a second delayed video signal, and
an adder for adding the second delayed video signal delayed video signal and the quantity of correction to generate a vertical contour corrected video signal.
As stated above, according to the eleventh aspect of the invention, a vertical contour correcting device having a unit which sequentially inputs extracted vertical contour components to circuits to extract a vertical contour correction signal and an adder for adding the vertical contour correction signal and a delay-adjusted present video signal comprises a group of a plurality of first delay units receiving the vertical contour components extracted by the extracting unit, a first minimum value detector receiving the vertical contour components outputted from the first delay unit group for outputting the minimum value thereof, and a group of a plurality of, two or more, second delay units for delay-adjusting the present signal, which can reduce enhancement of noise when an impulse type noise which is difficult to reduce with a horizontal low-pass filter causes a vertical contour component of the video signal to become much larger than horizontally adjacent pixels.
According to a twelfth aspect of the invention, in the eleventh aspect, the minimum value detector and the horizontal low-pass filter have equal horizontal delay times, and
the plurality of second delay units have a delay time equal to a sum of the horizontal delay time in the minimum value detector and the horizontal delay time in the horizontal low-pass filter.
As stated above, according to the twelfth aspect of the invention, the delay time used to detect the minimum value is equal to the delay time in the horizontal low-pas filter, and then the horizontal direction line vertical contour component outputted from the minimum value detector becomes the same horizontal direction line vertical contour component as the original contour. As a result, it is possible to reduce extension of the vertical contour correction signal to video originally not corrected.
According to a thirteenth aspect of the invention, in the first aspect, the quantity of correction varying unit further comprises a coefficient multiplier for varying the quantity of correction by multiplying the quantity of correction by a coefficient having a given value,
and wherein vertical contour enhancement of the video signal is varied with the quantity of correction varied with the coefficient to enhance only the vertical contour while suppressing enhancement of the noise.
As stated above, according to the thirteenth aspect of the invention, the quantity of correction is corrected with a coefficient, and then fine correction can be applied by devising the way of setting the coefficient.
According to a fourteenth aspect, in the thirteenth aspect, the coefficient is smaller than 1.
As stated above, according to the fourteenth aspect, the vertical contour enhancement processing in which the quantity of correction is set to be smaller than one prevents noise from being enhanced with the vertical contour.
According to a fifteenth aspect of the invention, in the fourteenth aspect, the correlation detector comprises,
a vertical contour component extracting unit for extracting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detector for detecting correlation between the detected horizontally adjacent vertical contour components,
and wherein the quantity of correction varying unit multiplies the detected horizontally adjacent vertical contour components by coefficients having different given values.
As stated above, according to the fifteenth aspect of the invention, vertical contour components adjacent in the horizontal direction are multiplied by coefficients with different values so that correction can properly be applied in accordance with the correlation between the vertical contour components, which is especially effective to prevent impulse noise.
According to a sixteenth aspect of the invention, in the fourteenth aspect, the correlation detector comprises,
a vertical contour component extracting unit for extracting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detector for detecting correlation between the detected horizontally adjacent vertical contour components,
and wherein the quantity of correction varying unit multiplies the detected horizontally adjacent vertical contour components by a coefficient having the same given value.
As stated above, according to the fifteenth aspect of the invention, horizontally adjacent vertical contour components are multiplied by the same coefficient to apply uniform correction, which is especially effective for prevention of step noise.
According to a seventeenth aspect of the invention, a vertical contour correcting method which corrects vertical contour components of a video signal to enhance vertical contour of the video signal comprises:
a correlation detecting step of detecting correlation between a noise component contained in the video signal and the detected vertical contour components; and
a quantity of correction varying step of varying the quantity of correction of the vertical contour components on the basis of the correlation;
thereby enhancing the vertical contour without enhancing the noise.
As stated above, according to the seventeenth aspect of the invention, the quantity of correction is varied in accordance with correlation between noise component contained in an input video signal and vertical contour components to correct vertical contour in accordance with the magnitude of the noise component, thus reducing enhancement of the noise caused by the vertical contour correction without considerably deteriorating the effect of the entire contour correction.
According to an eighteenth aspect of the invention, in the seventeenth aspect, the correlation detecting step comprises,
a vertical contour component detecting step of detecting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detecting step of detecting correlation between the detected vertical contour components adjacent in the horizontal direction.
As stated above, according to the eighteenth aspect of the invention, the quantity of correction is varied in accordance with correlation between horizontally adjacent vertical contour components extracted from an input video signal to correct the vertical contour components by detecting presence/absence of a noise component among or in the vicinity of the contour components, thus reducing enhancement of the noise caused by the vertical contour enhancement without considerably deteriorating the effect of the entire contour correction.
According to a nineteenth aspect of the invention, in the seventeenth aspect, the vertical contour correcting method further comprises a vertical contour correcting step of adding the corrected vertical contour components to the video signal to generate a second video signal with enhanced vertical contour.
According to a twentieth aspect of the invention, in the eighteenth aspect, the horizontal correlation detecting step comprises,
a sign extracting step of extracting signs of the vertical contour components adjacent in the horizontal direction, and
a sign comparing step of comparing the extracted signs,
wherein the quantity of correction varying unit varies the quantity of correction when the signs of the vertical contour components adjacent in the horizontal direction are inverted.
As stated above, according to the twentieth aspect of the invention, when a vertical contour component corrected in the opposite direction, due to noise, to the present video signal adjacent in the horizontal direction is extracted, the quantity of correction can be varied so as to reduce enhancement of the noise.
According to a twenty-first aspect of the invention, in the seventeenth aspect, the vertical contour component extracting step further comprises
a delayed video signal extracting step of extracting a delayed video signal from the video signal by delay-adjusting the video signal,
and wherein the vertical contour correcting method further comprises a vertical contour correcting unit for varying said video signal with the varied quantity of correction to generate a second video signal with enhanced vertical contour.
According to a twenty-second aspect of the invention, in the seventeenth aspect, the vertical contour correcting method further comprises a vertical contour component quantity checking step of comparing the vertical contour component with a given threshold,
wherein the vertical contour component quantity checking step does not allow the quantity of correction varying step to be executed when the vertical contour component is smaller than the threshold.
As stated above, according to the twenty-second aspect of the invention, the quantity of correction varying unit is not operated when a vertical contour component inputted to the vertical contour component correlation detector is smaller than a given threshold, and therefore even if a vertical contour component corrected in the opposite direction, due to noise, to horizontally adjacent video signal is extracted, it is possible to know whether it is caused by noise or is a vertical contour component of the original video signal to set the most proper quantity of correction for the vertical contour.
According to a twenty-third aspect of the invention, in the twentieth aspect, when the vertical contour component is smaller than the threshold, the vertical contour component quantity checking step generates a control signal to stop the quantity of correction varying step.
According to a twenty-fourth aspect of the invention, in a vertical contour correcting method for enhancing vertical contour components of a video signal,
the quantity of correction for enhancing the vertical contour components is varied on the basis of correlation between present video signals adjacent in horizontal direction and video signals with corrected vertical contour components.
As stated above, according to the twenty-fourth aspect of the invention, a vertical contour correcting device which enhances vertical contour components of a video signal is characterized by varying the quantity of correction in accordance with correlation between horizontally adjacent present video signals and the video signals with corrected vertical contour components, wherein when the vertical contour correction causes the magnitude relation between video signals adjacent in the horizontal direction to differ from that before correction, the quantity of correction can be varied to keep the linearity of the video in the horizontal direction.
According to a twenty-fifth aspect of the invention, a vertical contour correcting method which corrects vertical contour components of a video signal with a given quantity of correction to enhance vertical contour of the video signal comprises:
a vertical contour component extracting step of extracting a delayed video signal by delay-adjusting the vertical contour components from the video signal and the video signal;
a correcting step of varying the vertical contour components to generate a correction signal;
an adding step of adding the correction signal and the delayed video signal to generate a vertical contour corrected video signal;
a step of inputting video signal components adjacent in horizontal direction extracted from the detected delayed video signal and the vertical contour corrected video signal,
a comparing step of comparing magnitude relation between the delayed video signal components and magnitude relation in the vertical contour corrected video signal; and
a control step of varying the quantity of correction in the correcting step when the magnitude relation between the horizontally adjacent video signal components is inverse to the magnitude relation in the vertical contour corrected video signal, based on an output from the comparing step.
As stated above, according to the twenty-fifth aspect of the invention, it comprises a controller for varying the quantity of correction by the correcting unit when the magnitude relation between horizontally adjacent present video signals before correction is inverse to the magnitude relation between video signals after correction, and then the quantity of correction can be varied when the vertical contour correction causes the magnitude relation between horizontally adjacent video signals to differ from that before correction, thus keeping the linearity in the horizontal direction of the video.
According to a twenty-sixth aspect, a vertical contour correcting method which corrects vertical contour components of a video signal with a given quantity of correction to enhance vertical contour of the video signal comprises:
a vertical contour component extracting step of generating a delayed video signal by delaying the vertical contour components from the video signal and the video signal;
a first delay step of sequentially delaying the vertical contour components to generate a plurality of delayed vertical contour component signals;
a minimum value detecting step connected to the plurality of first delay units for detecting a minimum value among the plurality of delayed vertical contour component signals; and
a correcting step which uses the detected minimum value among the delayed vertical contour component signals as the quantity of correction.
As stated above, according to the twenty-sixth aspect of the invention, the minimum value is detected from among vertical contour components extracted from an input video signal by using a plurality of delay units and a minimum value detector and the detected minimum value is used as a correction signal, which reduces enhancement of noise when a vertical contour component of the video signal is much larger than horizontally adjacent pixels due to an impulse type noise which is difficult to reduce with a horizontal low-pass filter.
According to a twenty-seventh aspect, in the twenty-sixth aspect, the correcting step comprises,
a coring step of coring the minimum value of the delayed vertical contour component signals,
a horizontal low-pass filter step of applying horizontal low-pass filter to the cored minimum value of the delayed vertical contour component signals,
a coefficient step of multiplying the minimum value subjected to the horizontal low-pass filter by a given coefficient, and
a limit step of limiting band of the minimum value multiplied by the coefficient,
and wherein the vertical contour correcting method further comprises,
a second delay step of sequentially delaying the delayed video signal to generate a second delayed video signal, and
an adding step of adding the second delayed video signal delayed video signal and the quantity of correction to generate a vertical contour corrected video signal.
As stated above, according to the twenty-seventh aspect of the invention, a vertical contour correcting device having a unit which sequentially inputs extracted vertical contour components to circuits to extract a vertical contour correction signal and an adder for adding the vertical contour correction signal and a delay-adjusted present video signal comprises a first delay step receiving the vertical contour components extracted by the extracting unit, a first minimum value detector receiving the vertical contour components outputted from the first delay step for outputting the minimum value thereof, and a group of a plurality of, two or more, second delay units for delay-adjusting the present signal, which can reduce enhancement of noise when an impulse type noise which is difficult to reduce with a horizontal low-pass filter causes a vertical contour component of the video signal to become much larger than horizontally adjacent pixels.
According to a twenty-eighth aspect of the invention, in the twenty-seventh aspect, the minimum value detecting step and the horizontal low-pass filter step have equal horizontal delay times, and
the plurality of second delay steps have a delay time equal to a sum of the horizontal delay time in the minimum value detecting step and the horizontal delay time in the horizontal low-pass filter step.
As stated above, according to the twenty-eighth aspect, the delay time used to detect the minimum value is equal to the delay time in the horizontal low-pas filter step, and then the horizontal direction line vertical contour component outputted from the minimum value detector becomes the same horizontal direction line vertical contour component as the original contour. As a result, it is possible to suppress extension of the vertical contour correction signal to video originally not corrected.
According to a twenty-ninth aspect of the invention, in the seventeenth aspect, the quantity of correction varying step further comprises a coefficient multiplying step of varying the quantity of correction by multiplying the quantity of correction by a coefficient having a given value,
and wherein vertical contour enhancement of the video signal is varied with the quantity of correction varied with the coefficient to enhance only the vertical contour while suppressing enhancement of the noise.
As stated above, according to the twenty-ninth aspect of the invention, the quantity of correction is corrected with a coefficient, and then fine correction can be applied by devising the way of setting the coefficient.
According to a thirtieth aspect of the invention, in the twenty-ninth aspect, the coefficient is smaller than 1.
As stated above, according to the thirtieth aspect of the invention, the vertical contour enhancement processing in which the quantity of correction is set to be smaller than one prevents noise from being enhanced with the vertical contour. According
According to a thirty-first aspect of the invention, in the thirtieth aspect, the correlation detecting step comprises,
a vertical contour component extracting step of extracting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detecting step of detecting correlation between the detected horizontally adjacent vertical contour components,
and wherein the quantity of correction varying step multiplies the detected horizontally adjacent vertical contour components by coefficients having different given values.
As stated above, according to the thirty-first aspect of the invention, vertical contour components adjacent in the horizontal direction are multiplied by coefficients with different values so that correction can properly be applied in accordance with correlation between the vertical contour components, which is especially effective to prevent impulse noise.
According to a thirty-second aspect of the invention, in the thirtieth aspect, the correlation detecting step comprises,
a vertical contour component extracting step of extracting vertical contour components adjacent in horizontal direction from the video signal, and
a horizontal correlation detecting step of detecting correlation between the detected horizontally adjacent vertical contour components,
and wherein the quantity of correction varying step multiplies the detected horizontally adjacent vertical contour components by a coefficient having the same given value.
As stated above, according to the thirty-second aspect of the invention, horizontally adjacent vertical contour components are multiplied by the same coefficient to apply uniform correction, which is especially effective for prevention of step noise.